Between the main generator/gasifier systems, the generally preferred countercurrent gasifier and the cocurrent gasifier, the latter is preferred according to the invention for generating the lean gas. The generator gas obtained according to the principle of countercurrent gasification is of limited use since it can be used only for subsequent direct combustion because it has a high content of viscous pyrolysis products, such as tar, phenol and the like, which condense at temperatures below 400.degree. C.
The principle which is preferred according to the basic concept of the invention involves descending gasification, in which the dry zone and the pyrolysis zone are formed in the upper part of the reactor. According to preferred aspects of the present invention, in contrast to the countercurrent principle, air is fed in from above, directly after the pyrolysis zone. The combustion produces the necessary temperatures to cleave the descending low-temperature carbonization products from the pyrolysis zone into readily combustible gases. The remaining volatile substances are also gasified from the charcoal. Thus, no tar products enter the subsequent reduction zone.
Regarding the technological peculiarities of these gasification processes, reference is made to "Holzvergasung", Willy Bierter/Christian Gaegauf, Karlsruhe, 1982, page 52 et seq. Furthermore, the prior art in the area of gas generators includes German Patent 3,239,624, FIG. 1 to 3 and associated description, column 2, line 11 et seq and column 4, lines 41 to 7, page 10.
The stated patent describes five gasification principles, among which the cocurrent principle is most closely related to the invention. In order to carry out this gasification principle, the invention provides a generator whose elements and features have, in some cases been radically redesigned and in some cases, modified compared with the prior art, so that the generator process is based on a modified cocurrent principle.